Phase of transcranial alternating current stimulation modulates reaction time in working memory tasks

Area of Science:

• Neuroscience
• Cognitive Science
• Neuromodulation

Background:

• Theta-frequency transcranial alternating current stimulation (tACS) over the prefrontal cortex is investigated for its effects on working memory (WM).
• Inconsistent behavioral effects of tACS suggest that stimulation phase during task performance may be a critical variable.

Purpose of the Study:

• To determine if behavioral performance in working memory tasks is dependent on the phase of prefrontal theta-tACS.
• To explore the role of stimulation phase in modulating cognitive performance.

Main Methods:

• Twenty participants underwent two sessions of 4 Hz prefrontal tACS (active and sham) in a within-subject design.
• Participants completed a visuospatial change detection task (CDT) and a verbal N-back task.
• Phase-specific analyses using circular regression models examined the relationship between stimulation phase and behavioral outcomes (accuracy, reaction time).

Main Results:

• No significant overall differences in accuracy or reaction time between active and sham tACS were found.
• Phase-specific analyses revealed significant phase-dependent modulation of reaction time during active tACS compared to sham.
• This phase-dependent effect on reaction time was observed across difficulty levels in the CDT and in the 3-back condition of the N-back task, but not for accuracy.

Conclusions:

• Prefrontal theta-tACS can modulate working memory performance in a phase-dependent manner, even without significant average effects.
• The phase of stimulation is a crucial factor influencing reaction times in both visuospatial and verbal working memory tasks.
• Stimulation phase represents a potential source of variability in cognitive performance across different tasks.